Merge "libfdt: Make Fdt::root{,_mut}() infallible" into maindiff --git a/README.md b/README.md
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@@ -15,6 +15,7 @@
AVF components:
* [pVM firmware](pvmfw/README.md)
+* [Android Boot Loader (ABL)](docs/abl.md)
* [Microdroid](microdroid/README.md)
* [Microdroid kernel](microdroid/kernel/README.md)
* [Microdroid payload](microdroid/payload/README.md)
diff --git a/docs/abl.md b/docs/abl.md
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+# Android Bootloader (ABL)
+
+[ABL](https://source.android.com/docs/core/architecture/bootloader) is not a component of AVF, but
+it plays a crucial role in loading the necessary AVF components and initializing them in a correct
+way. This doc explains the responsibilities of ABL from the perspective of AVF.
+
+## pVM firmware (pvmfw)
+
+ABL is responsible for the followings:
+
+* locating pvmfw binary from the pvmfw partition,
+* verifying it as part of the [verified
+ boot](https://source.android.com/docs/security/features/verifiedboot) process,
+* loading it into memory, and
+* describing the region where pvmfw is loaded using DT and passing it to hypervisor.
+
+See [ABL Support](../pvmfw/README.md#android-bootloader-abl_support) for more detail.
+
+ABL is also responsible for constructing the pvmfw configuration data. The data consists of the
+following info:
+
+* DICE chain (also known as BCC Handover)
+* DTBO describing [debug policy](debug/README.md#debug-policy) (if available)
+* DTBO describing [assignable devices](device_assignment.md) (if available)
+* Reference DT carrying extra information that needs to be passed to the guest VM
+
+See [Configuration Data](../pvmfw/README.md#configuration-data) for more detail.
+
+## Android
+
+ABL is responsible for setting the following bootconfigs describing the status and capabilities of
+the hypervisor.
+
+* `androidboot.hypervisor.version`: free-form description of the hypervisor
+* `androidboot.hypervisor.vm.supported`: whether traditional VMs (i.e. non-protected VMS) are
+ supported or not
+* `androidboot.hypervisor.protected_vm.supported`: whether protected VMs are supported or not
+
+Thee bootconfigs are converted into system properties by the init process.
+
+See
+[HypervisorProperties.prop](https://android.googlesource.com/platform/system/libsysprop/+/refs/heads/main/srcs/android/sysprop/HypervisorProperties.sysprop)
+for more detail.
+
+
+
+
+
+
+
+
+
+